This invention relates to rotatable turbine blades and more particularly to a group of blades held on the rotor with pins. Rotatable blades with pin roots have been utilized in turbines for many years. The original pinned root blade groups were welded together. Later, when materials changed so that welding could no longer be utilized, electric discharge machining was utilized to manufacture the blade groups from a block of metal. The blade groups described hereinafter have improved vibratory and steady-state stress characteristics.
In general, a blade group which attaches to a disc disposed on the shaft of an axial flow turbine, when made in accordance with this invention, comprises a platform portion, multiple blade portions extending radially outwardly from the platform portion, and multiple root portions extending radially inwardly from the platform portion. The root portion comprises generally flat spaced-apart arcuate segments disposed normal to the axis of the shaft and the turbine rotor or disc has circumferential grooves which receive the root portion. Multiple pins extend axially through the root portions and the disc and the platform has a protrusion on one corner and a notch on the opposite corner so that the protrusion in one blade group fits the notch in adjacent blade group when a plurality of blade groups are disposed in a circular array on the rotor.